Rock drilling bit



Feb. 21, 1956 s, P. G. HUGLUND ETAL 2,735,656

ROCK DRILLING BIT Filed March 20. 1950 2 Sheets-Sheet 1 Fig, (Pr/or an)9- Z 1956 s. P. e. HOGLUND ETAL 2,735,656

ROCK DRILLING BIT Filed March 20, 1950 2 Sheets-Sheet 2 United StatesPatent ROCK DRILLING BIT Stig Per Gustav Hiiglund, Sandviken, and AndersGustav Kindahl, Sundsvall, Sweden, assignors to- Sandvikens JernverksAktiebolag, Sandviken, Sweden The most common type of rock drilling bitsfor percussion drilling comprises one or more inserts of hard metal orthe like fastened in grooves formed in the bit body in such a mannerthat the bottoms of the grooves are at right angles to the axis ofrotation of the drill bit.

Experience has proved that the best results are obtained when thecutting edges of the inserts of the said drill type are curved. However,due to this curved form the peripheral portions of the insert are, inrespect of the direction of drilling, weaker than the central portionsof the insert.

Further, experience has proved that the peripheral portions ofpercussion drilling bit inserts wear more rapidly than the portionscloser to the bit axis.

These circumstances involve that the said peripheral portions rapidlybecome completely worn down while the portions closer to the axis ofrotation of the drill bit still possesses sufiicient thickness andstrength. This is waste of expensive hard metal material because the bithas to be discarded although the cutting material has not been fullyutilized.

Due to the weakening of the peripheral portions cracks and rupturesusually occur in these portions.

Several attempts have been made to eliminate the said disadvantages.Thus the inserts have been made of compound material so as to render theperipheral portions harder and more durable than the central portions.Further, drill bits have been constructed comprising a greater number ofinserts disposed along the periphery of the bit than at the centralportion thereof. However, the manufacture of drill bits of this type israther complicated and expensive.

The principal object of the present invention is to provide rock drillbits which are not attended with the abovementioned draw-backs and whichare simple and inexpensive to manufacture.

The main feature of the drill bit according to the invention resides inthat the grooves which receive the inserts have such a form that theportions of the bottom of each groove, which are situated at or near thecentral axis in the boring direction, are located forwardly, in thedirection of boring, of the peripheral portions of the said bottom, andin that the base portion of the respective insert or inserts has or havea form corresponding to that of the bottoms of the grooves. Thereby anadvantageous distribution of hard metal is obtained which gives the newdrill bit a longer life than the drill bits of the hitherto knownconstructions provided with the same amount of hard metal.

According to the invention the longitudinal section of the bottom of thegrooves may be curved or have the form of angles or lines broken at twoor more points.

The invention will now be described more in detail with reference to theaccompanying drawings which show preferred embodiments of the invention.

Fig. 1 is an end view of a drill bit of a known construction providedwith only one insert.

Fig. 2 is a section along the line IIII in Fig. 1.

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Fig. 3 is a section, analogous to the section in Fig. 2, through a drillbit according to the present invention, illustrating how the bottom ofthe groove is curved in its longitudinal direction.

Fig. 4 is a view in the longitudinal direction of the groove of thedrill bit shown in Fig. 3, the insert being removed.

Fig. 5 is a section through a modified embodiment of the invention inwhich two inserts are accommodated in a groove with a curved bottom.

Fig. 6 is a section through an embodiment in which the bottom of thegroove has the form of an angle.

Fig. 7 illustrates an embodiment in which the longitudinal section ofthe bottom of the groove has the form of a line broken at two points.

Fig. 8 is an end view of a drill bit provided with three inserts, and

Fig. 9 is a section along the line IX-IX in Fig. 8.

As will be apparent from Fig. 2 the body 1 of the known drill bit has agroove with a straight bottom 2. Into the groove is inserted a hardmetal insert 3 having a straight base portion. The dotted line of thefigure indicates the contour line formed through normal wear of theinsert 3, whereby the peripheral portions 4 and 5 of the insert arealmost completely worn down, while the central portion of the insertstill has considerable thickness. Thus, the life of the known drill bitis predetermined by the peripheral portions of the insert which areweakened by the initial curved form of the cutting edge thereof, andtherefore a considerable part of the hard metal of the insert will bewasted. Moreover, cracks and ruptures in most cases occur approximatelyat 6 as a consequence of the heavy blows caused by the percussion boringoperation.

The drill bit shown in Fig. 3, which is constructed according to theinvention, has the same appearance as the known drill bit shown in Figs.1 and 2. However, in the body 7 of the new drill bit a groove '7 (Fig.4) is formed the bottom 7" of which is curved in such a way that theportion 8 of the bottom of the groove, which is situated at the centralaxis of the drill bit in the direction of boring of the bit (see arrowA), is ahead or in front of the peripheral portions 9 and 10 of the saidbottom. In this groove is fastened an insert 11 whose base portion has aform corresponding to that of the bottom 8 along the whole lengththereof. The dotted line of Fig. 3 indicates once again the contour lineresulting from normal wearing of the insert. In order to make clear theidea of the invention the insert 11 is shown as consisting of the sameamount of material as the insert 3 shown in Fig. 2. The form thataccording to the invention has been given to the bottom of the grooveand the base portion of the insert involves that the hard metal of theinsert can be considerably better utilized than in the case of the knowndrill bit shown in Figs. 1 and 2. As a consequence of the accumulationof material at the peripheral portions of the insert the risk of cracksand ruptures occurring in these portions is reduced.

Instead of the insert being formed as a single piece, two or more piecesor parts may be used placed in the same groove, as shown in Figs. 5-7.In Fig. 5 the groove has a round bottom considered longitudinally ofitself similarly as in the embodiment of Figs. 3 and 4, and is providedwith two inserts 12 and 13 having correspondingly round bottom surfacesto fit the groove. In the embodiments according to Figs. 5-7 the insertsare preferably interconnected by brazing with or without webbingsbetween them. If desirable an open clearance may be left between theadjacent ends of the inserts.

The longitudinal section of the groove of the embodiment shown in Fig. 6has the form of an angle the tip of which is directed in the boringdirection of the bit. Both 3 of the inserts (14 and 15) shown have astraight base portion and join each other at the tip of the angle.

The longitudinal section of the bottom of the groove may also have theform of a line broken at two or more points as shown in Fig. 7. In sucha case the inserts (17, 18, 19) preferably have the same length as thecorresponding portions of the bottom of the groove.

The invention may be adapted for most rock drilling bits with insertforms known per se, for example, bits provided with three or fourcutting edges, that is, so called three or four point bits. Figs. 8 and9 show as an example a bit 20 according to the invention provided withinserts 21, 22, and 23 arranged in radially extending grooves 23 thusproviding three cutting edges.

In all of the embodiments described above the inserts may advantageouslybe fastened in their grooves by braz- Rinsing holes and other detailsmay be arranged in usual ways.

It is to be understood that the invention is not limited to theparticular embodiments described and shown as various other embodimentsare possible within the scope of the invention.

Having now described our invention, what we claim as new and desire tosecure by Letters Patent is:

l. A rock drilling bit comprising a drill bit body having an elongatedgroove formed in its forward face considered in the direction ofdrilling, an elongated cutting insert of hard metal secured in saidgroove, said groove, in its longitudinal direction, being directedsubstantially transversely of the central axis of said bit body, saidgroove extending substantially through the central axis to the peripheryof said body, the bottom of said groove situated near said central axisbeing located forwardly in the drilling direction of the portions of thebottom located near the periphery of said bit body, said cutting inserthaving curved wear surfaces facing in the direction of drilling, theportions of said wear surfaces located at and near said central axisbeing located forwardly, in the direction of drilling, of the portionsof the wear surfaces located in the vicinity of the lateral periphery ofsaid drill bit body, the angle between a line tangent to the portion ofsaid wear surface most remote from said axis and said axis being greaterthan the angle between a line tangent to the portion of said bottom mostremote from said axis and said axis, said insert having a base portionhaving a form corresponding to that of the bottom of said groove,whereby the thickness of said insert, in the direction of drilling,toward the laterally remote portions of said insert is greater thantoward the center thereof.

2. A rock drilling bit as defined in claim 1, and in which the insertconsists of more than one piece of hard metal, and the bottom of thegroove is formed of at least two plane surfaces with an angletherebetween, the height of the cutting insert in the drilling directionbeing greater at the portion thereof most remote from said axis than atthe portion of said insert positioned closer to said axis.

3. A rock drilling bit as defined in claim 1, in which the insertconsists of more than one piece of hard metal.

References Cited in the file of this patent UNITED STATES PATENTS1,718,462 Hardsogg June 25, 1929 1,901,643 Harrington Mar. 14, 19332,306,598 Ellson Dec. 29, 1942 2,494,188 Meaney Jan. 10, l950 2,502,128Curtis Mar. 28, 1950 2,507,221 Phipps May 9, 1950 2,579,268 MalherbeDec. 18, 1951 FOREIGN PATENTS 18,443 Great Britain Aug. 7, 1913 130,187Sweden Nov. 28, 1950 423,647 Great Britain Feb. 5, 1935 669,636 GreatBritain Apr. 9, 1952 951,335 France Apr. 11, 1949

